Metal capacitor and method of making the same

ABSTRACT

A method of making a metal capacitor includes the following steps. A dielectric layer having a metal interconnection and a capacitor electrode is provided. Then, a treatment is performed to increase the dielectric constant of the dielectric layer surrounding the capacitor electrode. The treatment can be UV radiation, a plasma treatment or an ion implantation. Accordingly, the metal capacitor will have a higher capacitance and RC delay between the metal interconnection and the dielectric layer can be prevented.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to a metal capacitor and a method ofmaking the same, and more particularly, to a structure and a method ofimproving the capacitance of a metal-oxide-metal (MOM) capacitor.

2. Description of the Prior Art

As the complexity and integration of integrated circuits continues toincrease, the size of semiconductor elements becomes smaller andsmaller. This has led to a reduction in the overall size of capacitorswith the result that the corresponding capacitance is also reduced.Generally, there are three effective ways to improve the capacitancethrough circuit design. The first way is to decrease the separationbetween the capacitor electrodes. The second way is to increase thesurface area of each capacitor electrode. The third way is to use adielectric material with a high dielectric constant in the capacitordielectric layer.

Commonly used capacitors include the metal-insulator-metal (MIM)capacitor, metal-oxide-metal (MOM) capacitor and metal-insulator-silicon(MIS) capacitor. The fabricating process of a MOM capacitor can beintegrated with the interconnect process; hence no extra photomask isrequired. Therefore, the MOM capacitor is the most commonly usedcapacitor in the semiconductor field.

Methods to increase the capacitance of the MOM capacitor are well-knownin the art: for instance, arranging the capacitor electrodes in a stackstructure to replace the planar capacitors or placing the capacitorelectrodes in a comb-like structure to increase the surface area of thecapacitor electrode. However, because modern electronic devices arebuilt at the nano scale, the size of the MOM capacitor has to be scaleddown. Under this condition, increasing the surface area of the MOMcapacitor electrode can no longer provide enough capacitance.

As mentioned above, besides the surface area of the capacitor electrode,the capacitance of the capacitor is also in direct proportion to thedielectric constant of the capacitor dielectric layer. Therefore,increasing the dielectric constant of the capacitor dielectric layer isanother possible way to improve the capacitance of the MOM capacitor.

However, in order to avoid RC delay and parasitic capacitance, a metalwire with a low resistance is used in the metal interconnection and adielectric layer with low dielectric constant is positioned between themetal wires. To integrate the interconnect process, the MOM capacitorand the metal interconnection are usually formed in the same dielectriclayer. That is, the MOM capacitor is formed in the dielectric layer withlow dielectric constant in order to integrate the fabricating processand avoid RC delay. This, however, results in the capacitance of the MOMcapacitor being compromised.

Therefore, the reduced surface area of the capacitor electrode and thelow dielectric constant of the capacitor dielectric layer deterioratethe capacitance of the MOM capacitor. Accordingly, a method offabricating a metal capacitor which can both overcome the RC delay andimprove the capacitance is demanded.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a capacitorstructure and a method of making the same to maintain the capacitancewhen the MOM capacitor is scaled down.

According to a preferred embodiment of the present invention, a methodof forming a metal capacitor comprises: providing a dielectric layerhaving a first region and a second region; forming a metalinterconnection in the first region and forming a capacitor electrode inthe second region; and performing a treatment on the dielectric layer inthe second region to make a dielectric constant of the dielectric layerin the second region higher than a dielectric constant of the dielectriclayer in the first region.

According to anther preferred embodiment of the present invention, ametal capacitor structure comprises: a dielectric layer having a firstregion and a second region, wherein a dielectric constant of thedielectric layer in the second region is higher than a dielectricconstant of the dielectric layer in the first region; a metalinterconnection positioned in the first region; and a capacitorelectrode positioned in the second region.

The present invention features the use of treatments such as UVradiation, a plasma treatment or an ion implantation to increase thedielectric constant of the dielectric layer in the second region, whilethe dielectric constant of the dielectric layer in the first regionremains the same. In this way, the dielectric layer in the first regionmaintains a low dielectric constant to prevent RC delay raised betweenthe metal interconnection. The dielectric constant of the dielectriclayer in the second region is increased to improve the capacitance ofthe metal capacitor.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 to FIG. 4 are schematic diagrams depicting a method offabricating a metal capacitor.

FIG. 5 shows a schematic diagram illustrating the treatment performed toa dielectric layer stack.

DETAILED DESCRIPTION

FIG. 1 to FIG. 4 are schematic diagrams depicting a method offabricating a metal capacitor. As shown in FIG. 1, a dielectric layer 10is provided. A first region 20 and a second region 30 are positioned onthe dielectric layer 10.

The dielectric layer 10 can be formed on a semiconductor substrate (notshown) such as a silicon wafer, a silicon on insulator (SOI), a siliconon sapphire (SOS), a silicon on zirconia (SOZ), a doped or undopedsemiconductor, a silicon epitaxial layer supported by a semiconductorsubstrate, or the like. The semiconductor is not limited to silicon, butalso can be silicon-germanium, germanium, or germanium arsenide. Thedielectric layer 10 is a material that has a low dielectric constant,such as FLARE™, SiLK™, poly(arylene ether) polymer, parylene compounds,polyimide, fluorinated polyimide, hydrogen silsesquioxane (HSQ),methylsilsesquioxane (MSQ), fluorinated silicon glass (FSG),silicondioxide, nanoporous silica or teflon.

By performing an interconnect process, a metal interconnection 22 isformed in the first region 20 and a capacitor electrode 32 issimultaneously formed in the second region 30. One possible method offorming the metal interconnection 22 and the capacitor electrode 32 isillustrated as follows: first, a single-damascene opening or adual-damascene opening is formed in the dielectric layer 10 in the firstregion 20 and a capacitor electrode trench is formed in the dielectriclayer 10 in the second region 20 by the lithography process and etchingprocess, etc. After that, copper, or other metal with low resistance, isdeposited in the capacitor electrode trench positioned in the secondregion 30, and the damascene opening positioned in the first region 20.In this way, the metal interconnection 22 such as a single-damasceneinterconnection or a dual-damascene interconnection can be formed in thefirst region 20 and the capacitor electrode 32 can be formed in thesecond region 30. Finally, copper is planarized by a chemical mechanicalpolishing (CMP) process. At this point, the dielectric layer 10 in thesecond region 30 and the capacitor electrode 32 constitute a metalcapacitor 34. In addition, a barrier (not shown) such as Ti, TiN, TaN,WN, or the like can be formed before the metal interconnection 22 inorder to prevent the diffusion of copper. Furthermore, a cap layer 24such as a silicon nitride can be formed on the metal interconnection 22to avoid copper or other metals diffusing into a dielectric layerdirectly covering the metal interconnection 22. As fabricating processof the barrier and the cap layer should be familiar to those skilled inthe art, further description of the process is omitted for brevity.

According to different designs, the capacitor electrode 32 in the secondregion 30 can be at least two comb-like structures positioned oppositeto each other or other patterns complementary in their shapes. Thecapacitor electrode 32 can also be arranged to provide a stackedstructure after combining a set of capacitor electrodes formed indifferent dielectric layers.

Then, as shown in FIG. 2, a mask such as a photomask 50 is formed tocover the first region 20 and the second region 30 is exposed throughthe photomask 50. After that, a treatment 60 is performed to make thedielectric constant of the dielectric layer 10 in the second region 30higher than the dielectric constant of the dielectric layer 10 in thefirst region 20. At this point, the dielectric layer 10 in the secondregion 30 and the capacitor electrode 32 constitute a metal capacitor 36such as a MOM capacitor with a higher capacitance.

The treatment 60 may be UV radiation, a plasma treatment or an ionimplantation. The dielectric constant of the dielectric layer 10 in thesecond region 30 and the depth of dielectric layer 10 which isinfluenced by the treatment 60 can be adjusted by controlling durationof the treatment 60, energy of the treatment 60 or dosage of thetreatment 60. Furthermore, based on different dielectric materials,different treatments can be used to increase the dielectric constant.According to a preferred embodiment of the present invention, after thetreatment 60 is performed, the dielectric constant of the dielectriclayer 10 in the second region 30 is at least 10% higher than thedielectric constant of the dielectric layer 10 in the first region 20.Finally, as shown in FIG. 3, the photomask 50 is removed.

According to another preferred embodiment of the present invention, thetreatment 60 can also be applied to dielectric material 10 in the secondregion 30 before the metal interconnection 22 and the capacitorelectrode 32 are formed. According to another preferred embodiment ofthe present invention, the treatment 60 can be replaced by the followingmethod: removing the dielectric layer 10 in the second region 30 andfilling the second region 30 by a dielectric material with a higherdielectric constant before the interconnection 22 and the capacitorelectrode 32 are formed.

As shown in FIG. 4, a third region 40 can also be set on the dielectriclayer 10. The third region 40 is a non-critical region such as aperipheral circuit, a logic IC or other iso-region (region havingisolated patterns). Elements in the non-critical region can be formed bycombining the interconnect process or other semiconductor processes. Thetreatment 60 can be performed on the dielectric layer 10 in the secondregion 30 and in the third region 40 simultaneously. Through the UVradiation, the plasma treatment or the ion implantation, the mechanicalstrength of the dielectric layer 10 in the third region 40 becomesgreater than the mechanical strength of the dielectric layer 10 in thefirst region 20.

For a dielectric layer stack (structure formed by a plurality ofdielectric layers), it is noteworthy that the treatment 60 can also beperformed after each metal interconnection 22 and capacitor electrode 32is formed in each dielectric layer. FIG. 5 shows a schematic diagramillustrating the treatment performed on a dielectric layer stack.

To simplify the illustration, a same numeral is designated for each sameelement. Assume the capacitor electrodes are formed in every dielectriclayer from the n^(th) layer to the (n+m)^(th) layer. As shown in FIG. 5,the metal interconnection 22 and the metal capacitor 34 are formed inthe n^(th), (n+1)^(th) . . . (n+m)^(th) layer. After that, a mask suchas a photomask 50 is formed on the (n+m)^(th) layer. Then, the treatment60 is performed. By adjusting energy of the UV radiation, the plasmatreatment or the ion implantation, the dielectric constant in the secondregion 30 in every dielectric layer can be increased: for instance,implanting ions into the (n+m)^(th) layer with strongest energy,implanting ions into the (n+1)^(th) layer with stronger energy andimplanting ions into the n^(th) layer with weak energy. In anotherexample, the UV radiation is performed for longer period of time toirradiate the n^(th), (n+1)^(th) . . . (n+m)^(th) layers. The advantageof this embodiment is that, instead of performing the treatment 60immediately after the metal interconnection 22 and the metal capacitor34 are formed in one dielectric layer, the treatment 60 can be performedby using only one photomask 50 when all the interconnections 22 and themetal capacitor 34 are formed in every dielectric layer. In this way,the product cost can be reduced.

The above-mentioned method is not limited to be utilized on the MOMcapacitor. After adjusting the fabricating steps, the present inventioncan be applied to the MIS capacitor or the MIM capacitor. In addition,the dielectric layer 10 is not limited to be formed on the semiconductorsubstrate; other material which can support the dielectric layer 10 suchas a PCB can also be used.

The feature of the present invention is that a second region 30 is seton the dielectric layer 10 having a low dielectric constant. Byperforming the treatment 60 on the second region 30, the dielectricconstant of the dielectric layer 10 in the second region 30 can beincreased while the dielectric constant of the dielectric layer 10 inthe first region 30 is maintained the same. That is, the dielectriclayer 10 surrounding the metal interconnection 22 still has a lowdielectric constant. Therefore, the RC delay can be prevented and thecapacitance of the metal capacitor 34 is increased. In addition, themechanical strength of the dielectric layer 10 in the third region 40(non-critical region) is increased after the treatment 60. Therefore,the non-critical region can avoid damage during the followingfabricating steps such as package or wire bonding.

A metal capacitor is also provided in the present invention. As shown inFIG. 4, a metal capacitor structure includes a dielectric layer 10having a first region 20, a second region 30 and a third region 40. Thedielectric layer 10 is a material having a low dielectric constant suchas FLARE™, SiLK™, poly(arylene ether) polymer, parylene compounds,polyimide, fluorinated polyimide, hydrogen silsesquioxane (HSQ),methylsilsesquioxane (MSQ), fluorinated silicon glass (FSG),silicondioxide, nanoporous silica or teflon.

The dielectric constant of the dielectric layer 10 in the second region30 is higher than the dielectric constant of the dielectric layer 10 inthe first region 20. The mechanical strength of the dielectric layer 10in the third region 40 is greater than the mechanical strength of thedielectric layer 10 in the first region 20. The metal capacitor furtherincludes a metal interconnection 22 positioned in the first region 20, acapacitor electrode 32 positioned in the second region 30 and anon-critical region such as a peripheral circuit, a logic IC or otheriso-region positioned in the third region 40. A cap layer 24 such assilicon nitride can optionally cover the metal interconnection 22.

In addition, the capacitor electrode 32 and the dielectric layer 10 inthe second region 30 constitute a metal capacitor 36 such as a MOMcapacitor. The metal interconnection 22 can be a single-damasceneinterconnection or a dual-damascene interconnection. Furthermore, thedielectric layer 10 can be positioned on a semiconductor substrate suchas a silicon wafer, a silicon on insulator (SOI), a silicon on sapphire(SOS), a silicon on zirconia (SOZ), a doped or undoped semiconductor, asilicon epitaxial layer supported by a semiconductor substrate, or thelike.

All in all, in order to avoid the parasitic capacitance between themetal interconnection, the dielectric layer with low dielectric constantis often used. However, to increase the capacitance of the metalcapacitor, a special fabricating method and a novel dielectric layerstructure is provided in the present invention. That is, the capacitorelectrode is located in a region having a high dielectric constant, andthe fabricating method of the capacitor electrode is integrated with theinterconnect process. In one aspect, the RC delay can be avoided. Inanother aspect, the capacitance of the metal capacitor can beeffectively increased. Furthermore, since the mechanical strength in thenon-critical region is increased, a better support is provided for theelements on the non-critical region for following processes.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

What is claimed is:
 1. A method of forming a metal capacitor,comprising: providing a dielectric layer having a first region and asecond region; after forming the dielectric layer forming a dualdamascene metal interconnection in the first region and forming adamascene capacitor electrode in the second region, and forming a caplayer over both dielectric layer regions; and performing a treatment onthe dielectric layer while the cap layer remains in the second region tomake a dielectric constant of the dielectric layer in the second regionhigher than a dielectric constant of the dielectric layer in the firstregion.
 2. The method of claim 1, wherein the treatment comprises a UVradiation, a plasma treatment or an ion implantation.
 3. The method ofclaim 2, wherein the dielectric constant of the dielectric layer in thesecond region can be adjusted by controlling duration of the treatment,energy of the treatment or dosage of the treatment.
 4. The method ofclaim 1, wherein the treatment is performed after the metalinterconnection and the capacitor electrode are formed.
 5. The method ofclaim 1, wherein the treatment is performed after a mask is formed onthe first region and the second region is exposed through the mask. 6.The method of claim 1, wherein the dielectric layer further comprises athird region, and the treatment is performed on the dielectric layer inthe third region and the dielectric layer in the second regionsimultaneously to improve the mechanical strength of the dielectriclayer in the third region.
 7. The method of claim 6, wherein the thirdregion comprises a non-critical region.
 8. The method of claim 1,wherein a cap layer is positioned on the metal interconnection.
 9. Themethod of claim 1, wherein the capacitor electrode and the dielectriclayer in the second region constitute a metal-oxide-metal (MOM)capacitor.